The present invention relates generally to systems and methods for manufacturing absorbent garment cores. More specifically, the present invention relates to a system and method for providing feedback control for the deposition of superabsorbent particles and other particulate and fibrous additives into a dry-formed, absorbent core material.
A continuing problem with the manufacture of high integrity tow-based fibrous cores has been to provide the SAP into the fibrous web in a controlled manner. Typical known processes for creating a conventional fluff pulp/SAP core use a large forming chamber to blend the SAP with the fluffed pulp, then convey this blend onto a drum or screen by using a vacuum. The drum or screen has forming pockets that form the fluff pulp/SAP material into the desired shape and the formed cores then are deposited for integration into absorbent products. Such methods have been found to be inefficient during startup and transitions in the manufacturing line speed because they require a relatively large amount of time to provide a stabilized mixture of SAP and fluff pulp, leading to the creation of a large number of scrap products until stabilization.
Other feeding systems use fixed-size moving mechanical gates that provide a uniform amount of SAP to the absorbent core, such as is disclosed in U.S. Pat. No. 6,139,912 to Onuschak et al., which is incorporated herein by reference in its entirety and in a manner consistent with the present invention. Although such devices may be suitable for providing an even flow of SAP or other powdered and particulate additives to absorbent cores, they rely on relatively complex feeding machinery, including a rotary valve that uses a pneumatic SAP conveyor to return undistributed SAP back to a supply container. Pneumatic conveyors typically require a relatively long time to become pressurized and to convey the SAP, causing inefficiencies during transitional phases, such as when the machine operating speed varies, such as during start-up and shut-down, or when it is desired to change the amount of SAP being fed to the core. The additional parts of such feeders may also be expensive and subject to wear and other service problems. Similar devices, having similar deficiencies, are disclosed in U.S. Pat. No. 4,800,102 to Takada, which is incorporated herein by reference in its entirety and in a manner consistent with the present invention.
Still other feeding systems use pneumatic particle projectors that use pressurized gas to convey the SAP to the surface of the absorbent core. Such devices are disclosed, for example, in U.S. Pat. No. 5,614,147 to Pelley and U.S. Pat. No. 5,558,713 to Siegfried et al., which are incorporated herein by reference in their entirety and in a manner consistent with the present invention. Such systems rely on relatively complex air conveyors, that may be susceptible to blockage and may not efficiently accommodate as wide a variety of particulate, powder and fibrous materials as other systems due to their relatively small passage sizes. Such systems may also require a relatively long time to stabilize, leading to inefficiencies during transitional phases.
However, such feeding systems have a number of shortcomings. First, the mixture still is subject to local concentrations and shortages of SAP, often resulting in a rejection of a considerable amount of the material during quality assurance processes. Second, such feeding systems cannot be controlled accurately enough to provide concentrations and shortages of SAP when they are desired.
Another shortcoming often inherent to known feeding systems is that such feeding systems typically can not be accurately controlled to accurately provide reduced SAP amounts that are necessary during transitional phases, leading to cores having undesirable concentrations of SAP manufactures during these transitional phases of operation. Typical known methods and systems to control the amount of SAP provided during these transitional phases generally are unable to adapt the deposition rate of SAP to the changing speeds of these transitional phases. Likewise, the devices used in these feed back systems often are vendor-dependent and therefore are difficult to adapt, if at all, to different operations of these feeding systems.
These are just a few of the disadvantages of the prior art that the preferred embodiments seek to address.
It would be desirable to provide an apparatus and method for depositing particulate matter, such as superabsorbents, into an absorbent core whereby the amount and position of the additives can be controlled with relative accuracy. It also would be desirable for such an apparatus and method to be able to deposit particulate matter in a manner that fewer rejected products are manufactured during transitional phases, such as startup, stopping and assembly line speed changes. Still further, it would be desirable for such an apparatus and method to be efficient, easy to operate, and capable of operating at high line speeds.
In accordance with these and other features of various embodiments of the invention, a system for synchronizing a deposition of particulate matter into a supply of fibrous material during a transition in a line speed of the fibrous material is provided. The system includes a feed tray having an outlet positioned above the supply of fibrous material, and a vibrator coupled to the feed tray for vibrating the feed tray, wherein when the vibrator vibrates the feed tray particulate matter in the feed tray is deposited onto the supply of fibrous material at a deposition rate substantially proportional to a vibratory motion of the vibrator and when the vibrator does not vibrate the feed tray substantially no particulate matter in the feed tray is deposited onto the supply of fibrous material. The system further includes a programmable logic controller coupled to the vibrator, wherein the programmable logic controller is adapted to control the vibratory motion of the vibrator to affect a transition in the deposition rate that is substantially proportional to the transition in the line speed.
These and other features of the invention will be readily apparent from the Detailed Description that follows, along with reference to the drawings appended hereto.